1. Field of the Invention
The present invention relates to an apparatus for dehydrating and drying by rotating a drum about an approximately horizontal rotary axis such as a drum drier or a drum washer-drier. More specifically, the present invention relates to a method and mechanism for reducing vibration of the drum drier or the drum washer.
2. Description of the Background Art
A drum washer-drier performing washing to drying by a single drum has been known. A representative drum washer-drier has such a structure in that the drum rotates about a horizontal axis in a water tank, and functions from washing, rinsing, dehydration to drying can be performed by the single drum.
Structure of a conventional drum washer-drier will be described in the following. FIGS. 19 and 20 show a first example of the prior art. Referring to FIGS. 19 and 20, the conventional drum washer-drier includes a drum 171 having a number of small holes 2 for receiving and rotating laundry, and a water tank 3 enclosing drum 171. At the central portion of water tank 3, a horizontal rotary axis 4 having one end fixed at the center of drum 171 is rotatably supported. At the other end of rotary axis 4, a drum pulley 5 is fixed. A driving motor 6 is attached to the lower surface of water tank 3, and a motor pulley 7 provided on the rotary axis of driving motor 6 is operatively coupled to drum pulley 5 by means of a belt 8. Water tank 3 is held in an outer tank 9. Water tank 3 is resiliently supported in outer tank 9 by means of a plurality of tension springs 30 suspended from an internal upper surface of the box of outer body 9. Further, water tank 3 is held by a plurality of dampers 31 provided between the lower portion thereof and an inner bottom of external box of outer tank 9. Vibration of water tank 3 is attenuated by tension spring 30 and dumper 31.
A fluid balancer 122 is fixed on the periphery at a front surface of drum 171, so as to reduce vibration at the time of dehydration. As means for reducing vibration at the time of dehydration, provision of a weight on a front side surface of water tank 3 has been known, other than fluid balancer attached to drum 171.
At a front surface of outer tank 9, there is a door 16 for putting laundry in. Between water tank 3 and outer tank 9 at this portion, a bellows type door packing 17 is provided and when door 16 is closed, the inside of water tank 3 comes to be water tight, because of the door packing 17. At the bottom surface of external box of outer tank 9, there are a plurality of legs 20 for supporting the washer as a whole on a floor. At a lower portion of water tank 3, a drain valve 19 for draining water at the time of dehydration is provided. Further, there are drying air duct 241 for guiding drying air to water tank 3, a drying heater 214 provided in drying air duct 241, and a heat exchanger for 215 for removing moisture arranged on drying air duct 241. Motor 6, drain valve 19, a water feed valve, not shown, heater 214 and the like are all controlled by a control circuit 118 for controlling operations in various steps. Further, on an inner peripheral surface of drum 171, there is provided a buffer 21 for tumbling, which will be described later.
Another example of a conventional drum washer-drier is shown in FIG. 21. In this figure, portions corresponding to those of FIGS. 19 and 20 are denoted by the same reference characters. These have similar functions. Therefore, detailed description thereof will not be repeated.
In the example shown in FIG. 21, water tank 3 is resiliently supported on the inner portion of outer tank 9 by means of a plurality of antivibration legs 31 each including a compression spring and a damper. Antivibration leg 33 is fixed on the lower portion of water tank 3 and on the bottom surface of the box of outer tank 9, with antivibration rubber 34 interposed.
These conventional drum washer-driers operate in the following manner.
In the step of washing, laundry and water are put in drum 171, and drum 171 is rotated at a low speed by driving motor 6. Laundry in drum 171 is lifted up by a baffle 21 by the rotation of drum 171 and falls by the weight of itself (hereinafter, this operation will be referred to as "tumbling"), and washing is performed by the mechanical force thereof.
In the step of dehydration, first, water is drained by opening drain valve 19. Thereafter, drum 171 is rotated at a high speed about the horizontal rotary axis, water in the laundry is removed by centrifugal force, and the water is further removed out from drum 171 through small holes 2. At that time, because of bias of the laundry in drum 171, vibrating body including drum 171, driving motor 6 and water tank 3 vibrates, and reduction of this vibration is a problem. In the washer having fluid balancer 122 such as shown in FIGS. 19 to 21, fluid balancer 122 functions in the following manner. A prescribed amount of fluid is sealed in fluid balancer 122. When the number of rotation of drum 171 exceeds a resonance rotation number, the fluid immediately moves to the other side of the biased portion causing imbalance, adjusting balance. Thus vibration at the time of dehydration caused by imbalance of laundry can be prevented.
For washers which do not have a fluid balancer, a weight may be provided on water tank 3, as already mentioned. The weight reduces vibration of the vibrating body caused by bias of the laundry. However, the weight is of considerable weight, e.g. about 16 kg. Consequently, the weight of the vibrating body as a whole is so increased that it becomes necessary to make the structure of outer tank 9 robust. This leads to increase in weight of the product as a whole (heavier than 80 kg), and handling of the product during delivery becomes troublesome. Further, depending on the structure of houses, it may be necessary to reinforce the floor so that it can withstand the weight of the drum washer-drier at the time of installation. This is the reason why attenuation of vibration using fluid balancer has been adopted as a preferable measure.
As for the step of drying, air heated by heater 214 is fed to drum 171 to drying air duct 241, while the laundry is tumbled with the moisture removed by heat exchanger 215.
In the drum washer-drier shown in FIGS. 19 and 20, drum 171 rotates about horizontal rotary axis 4. Therefore, sometimes, water tank 3 vibrates considerably because of bias of laundry in drum 171. The vibration of water tank 3 is transmitted to the body of outer tank 9, that is, the washer as a whole, through tension springs 30. The magnitude of transmitted force at that time is in proportion to spring constant of tension springs 30. In order to reduce vibration transmitted to the washer as a hole, spring constant of tension spring 30 should be made smaller. However, spring constant of tension spring 30 has the following restriction.
When water is held in water tank 3, water tank 3 lowers against tensile force of tension spring 30. The amount of lowering is in inverse proportion to the spring constant of tension spring 30. The amount of lowering of water tank 3 is limited because of the dimension or specification of the product, and it cannot exceed a certain value. Therefore, spring constant of spring 30 cannot be set smaller than a prescribed value because of the limit. Accordingly, vibration of water tank 3 is transmitted to the washer as a whole with considerable vibration transmitting force, so that the floor itself vibrates. In the worst case, the house would eventually vibrate because of the vibration of the washer, causing problems of noise and dissatisfaction of the user.
In the drum washer-drier shown in FIG. 21, water tank 3 is not lifted by tension spring. Therefore, there is not the limit imposed by the spring constant of tension spring. In this type of washer, the problem is spring constant of antivibration rubber 34. In the example shown in FIG. 21, when the spring constant of antivibration rubber 34 is reduced to some extent, transmission of vibration of water tank 3 to outer tank 9 can be reduced. However, the spring constant of antivibration rubber 34 has the following restriction.
In the example shown in FIG. 21, when vibration is caused by bias of laundry, water tank 3 vibrates not only in the upper and lower directions but also left and right as well as front and rear directions. Antivibration rubber 34 prevents all these vibrations. However, in that case, load not only in the compressing direction but also in the shearing direction are imposed on antivibration rubber 34. In order to prevent breakage of antivibration rubber 34 by shear load, the hardness of antivibration rubber 34 should be extremely high. However, this increases spring constant of antivibration rubber 34. This results in much transmission force of vibration to the floor.
Japanese Patent Laying-Open No. 56-158692 proposes a solution of the problem of the prior art shown in FIGS. 19 and 20. Outline of the disclosure of Japanese Patent Laying-Open No. 56-158692 is shown in FIG. 22. Referring to FIG. 22, the washer-drier includes a plurality of rods 704 suspended from a lower portion of an upper surface of outer tank 9 and each having a spring receiving portion 710 at a lower tip end; a suspending fitting 706 fixed on water tank 3; a lower slider 712 fitted with suspended fitting 706 and having an opening through which the lower end of the rod 704 is slidably inserted; and a compression spring 708 for preventing vibration fitted between suspended fitting 706 and spring receiving portion 710 at the lower tip end of rod 704. Rod 704 is supported by an upper slider 702 at its upper end, which upper slider has a spherical portion conforming to a corner plate having a spherical portion formed at the lower portion of the upper surface of outer tank 9. In FIG. 22, same portions as those shown in FIGS. 19 and 20 are denoted by the same reference characters. The functions are the same. Therefore, detailed description thereof is not repeated here.
As shown in FIG. 22, in this example, water tank 3 is resiliently supported by rod 704, compression spring 708 and suspended fitting 706, and vibration is attenuated by further providing a damper 31 at a lower portion, besides spring 708. In this structure, when the water fed to water tank 3 increases, compression spring 708 is compressed gradually, and if the water exceeds a certain amount, the spring attains fully compressed state. At that time, water tank 3 is directly supported by rod 704 and suspended fitting 706, and it does not go lower than that position, even when spring 708 has small spring constant. Accordingly, the spring constant of spring 708 can be made smaller than in the prior art examples shown in FIGS. 19 and 20.
In such an example, an isolated and independent dumper 31 is provided between water tank 3 and inner bottom of outer tank 9. Therefore, vibration of water tank 3 is transmitted to outer tank 9 through the dumper, and directly to the floor through legs 20. Therefore, sufficient reduction of vibration transmitted to the floor cannot be realized.
Another problem related to vibration in the step of drying in the conventional washer is as follows. In the conventional drum washer-drier having fluid balancer 122 such as shown in FIGS. 19 and 20, in the step of drying, heated air is fed to water tank 3 through drying air duct 241 while drum 171 is rotated at a low speed, so as to dry the laundry in drum 171. At this time, fluid sealed in fluid balancer 122 rotating about the horizontal axis is distributed in fluid balancer 122 by centrifugal force when the number of rotation exceeds a prescribed number, imposing load in radial direction to fluid balancer 122, while it stay at a lower portion when rotation speed is low, imposing load on fluid balancer 122 in gravity direction.
As is well known, fluid balancer 122 is generally formed of a synthetic resin. Change in temperature during the step of drying may soften the synthetic resin, and it loses stiffness it has at the room temperature. In that case, it is possible that fluid balancer 122 may be deformed by the load caused by the fluid therein, when fluid balancer 122 rotates both at a high speed and at a low speed. Further, similar problem is caused by swelling pressure of fluid sealed in fluid balancer 122.
Japanese Patent Laying-Open No. 4-332596 proposes a solution of this problem. Here, a fixing boss extending in radial direction only is provided on fluid balancer 122, and a space is provided between the fluid balancer and the outer periphery of the drum for absorbing swell when fluid balancer 122 swells in the radial direction, so that pressure is not applied to the screw portion for fixing. This prevents the screw from becoming loose.
However, the proposal of Japanese Patent Laying-Open No. 4-332596 still has a problem to be solved. As is well known, generally, the fluid balancer is formed of a synthetic resin, and a hollow annular body is formed by joining and thermally welding openings of two annular grooves. These two annular concave grooves have different thicknesses, for example, they may have different rates of expansion. Amount of deformation of concave grooves differ because of the different rates of expansion, and therefore there is a stress at the welded portion, promoting breakage of the fluid balancer. This problem is encountered not only in the drum washer-drier but also in a drum drier.
When the vibration of water tank 3 is to be reduced by using the fluid balancer, there is also the following problem. Fluid balancer 122 does not function until rotation number of drum 171 exceeds the resonance rotation number, because of its operation characteristic. Therefore, in the washer-drier of the type in which drum 171 rotates horizontally, in the initial stage of dehydration, the resonance rotation number is exceeded with the fluid in fluid balancer still biased at a portion in the peripheral direction, generating a formidable vibration at that time. Therefore, it is difficult to simply replace the weight by a fluid balancer.
Japanese Patent Laying-Open No. 4-240481 proposes a solution to this problem. In this proposal, the fluid balancer is divided in radial direction, with mutually different inner circulation resistances. This prevents the fluid sealed in each of the divided portion from being biased at one portion in the peripheral direction, so that the vibration near resonance rotation number is suppressed.
However, in the technique disclosed in Japanese Patent Laying-Open No. 4-240488, for the fluid in the fluid balancer to be lifted against gravity, quite high a circulation resistance is necessary. This degrades balance adjustment function, which is the inherent function of the fluid balancer. The balance adjusting function refers to the function of the internal fluid concentrated on the opposite sides of the biased portion causing imbalance when resonance rotation number is exceeded, for adjusting balance. More specifically, if the inner circulation resistance is too high, the fluid in fluid balancer does not move fast enough when the rotation speed of the drum exceeds the resonance rotation number, taking much time in adjusting balance. As a result, considerable vibration is generated near the resonance rotation member.